Known taut wire security fences typically consist of a plurality of detection zones, with each detection zone comprising a pair of spaced anchor posts, a plurality of taut wires tensioned between the anchor posts by anchoring means, and a sensor post located between the anchor posts having mounted thereon a multiplicity of sensors, each of which is coupled to a taut wire. An inherent limitation of this type of known fence is that it is relatively insensitive to intrusions which occur close to the anchor post, i.e. such fences have a "dead zone" associated with each anchor post.
This problem is overcome by the taut wire security fence disclosed in U.S. Pat. No. 4,829,287, (Kerr et al), granted to the assignee of this application. The fence disclosed by Kerr et al comprises a plurality of detector posts, each of which includes anchor/sensor means which both anchor the taut wite under tension and act as intrusion sensors. Kerr et al also disclose the use of a partially conductive elastic sensing element, whose resistance decreases with an increase in pressure. This sensing element is used in conjunction with a sensor bar mechanism which, when subjected to a change in lateral tension of a taut wire, compresses the sensing element. This type of sensing mechanism possesses a number of advantages over other prior art sensors, but the non-linear behaviour of the sensing element necessitates the use of sophisticated signal processing electronics.
Another problem with some prior art systems is that they typically utilize a plurality of wire guiding devices comprising a helical coil and a rod. These devices have a major disadvantage, in that they can be removed from the system without triggering an alarm by slowly rotating the coil in an upward direction.